Systems for the packaging and disposal of nuclear wastes are known in the prior art. Some of these systems utilize concrete storage modules which contain and store containers of radioactive waste that have been deposited and immobilized therein. Examples of such modules are disclosed in U.S. Pat. No. 4,681,706, assigned to the Westinghouse Electric Corporation. After these modules have been loaded with waste containers and closed up, they may be stored in a radioactive waste facility. However, when waste containers are deposited in the storage module, a void space is often created within the module. This void space is undesirable because liquids originating either from the waste within the packages or from outside the storage module can collect in the void space and weaken the waste containers or the walls of concrete module. Ultimately, these liquids can provide a path for the migration of radionuclides out of the module.
Previously in such prior art storage modules, the void space created between the waste containers and the module inner wall was filled with a cementitious material that would harden into a continuous solid. Typically, a grout formed from a Portland-based cement was used for this purpose. After the cement or grout was allowed to harden, the completed modules were carried from the area where they were loaded within a disposal site for storage for an indefinite period of time. The modules must be stable and durable structures, since storage periods of up to 200 years or more are necessary, depending on the type of radioactive waste and its half-life.
A common method of disposing the modules is to bury them in specially prepared underground disposal sites. Such a disposal site may comprise a trench having a flat floor with a monitoring system incorporated therein to periodically monitor if any water is within the trench and to determine whether or not radioactive substances have somehow leaked from the modules. A layer of gravel is deposited over the floor for drainage, and the modules are stacked over the gravel layer in mutuallY adjoining columns. The stacked columns of modules are then covered by a plurality of layers of soils and sands. An example of such a disposal site is also disclosed in U.S. Pat. No. 4,681,706. After the stacked modules have been completely covered over, they may be stored indefinitely until the radioactive material contained within them decays into harmlessness.
Although the storage modules are formed of reinforced and relatively thick concrete to make them mechanically strong and impervious to water, a problem can arise if the concrete forming the module should develop a crack. Such a crack might result from a seismic disturbance, a shifting of the modules within the soil, from subsidence, or a dropping of one of the modules during the stacking operation. The cementitious grout used as an additional barrier to immobilize the radioactive package within the module could also develop a crack which could then allow water and possibly waste material to pass through the walls of the storage modules. Thus, while a concrete module with a cementitious grout is, under most circumstances, capable of safely storing radioactive waste containers for an indefinite period of time, there are conditions which could result in a crack that could leak to a leakage condition. If such a leak should develop, then the monitoring system should notify an operator at the disposal site that an unacceptable situation has developed which needs to be remedied. The storage modules could be uncovered and the faulty storage module responsible for the leakage could then be removed from the site for repair or replacement. However, the hardened grout in such a module could hinder the removal of the leaking waste packages, making it necessary to break up the hardened grout and possibly even the walls of the storage module and the waste containers just to get at the waste. Another shortcoming associated with the use of grout is the tendency of the some of the lighter weight waste containers to float upwardly when the heavy grout is poured into the module. When this occurs, it becomes necessary for an operator to push the container or containers back down into the module interior before the grout hardens so that the module lid will fit properly. The added step caused by such unwanted floating slows up the module packing procedure, and increases the amount of radiation exposure to the operators.
Before the utilization of storage modules as described above, other unsatisfactory methods for the permanent disposal of nuclear waste had been attempted. One such method included the simple containment of nuclear waste in 55-gallon steel drums which were transported to a remote burial site. Such a system turned out to be entirely inadequate because water would accumulate around the drums due to the "bathtub effect" and corrode and collapse them, which could result in the radioactive contamination of the ground water coming in contact with the drums. Other methods of disposal have dropping barrels or modules to the ocean floor for indefinite storage. Unfortunately, these methods are disadvantageous in that the barrels or modules are subject to corrosion and breakage due to corrosive salts and high ocean pressures which can result in leakage of the radioactive wastes. One type of packaging for ocean disposal of radioactive wastes is disclosed in U.S. Pat. No. 4,377,509, issued Mar. 22, 1983 to Haynes et al., wherein a concrete shell is provided with waste receptacles such as steel drums with a filler disposed between the drums and the shell. When this concrete shell is dropped to the ocean floor, water enters the shell and reacts with the filler to form a hardened cement-like material that immobilizes the waste drums within the shell, while a pressure compensation system prevents the shell from collapsing under ocean pressures as the package drops. However, as in the above-discussed storage modules, the package is stored for an indefinite period with a hardened cement filler between the cement shell and the waste receptacles, and is thus subject to the same disadvantages relating to the potential for cracks and the difficulty in retrievability associated with a cement filler.
Other storage methods are known for permanently storing waste material in a subterranean depository which fixes the waste material within a solid formed by adding a composition to liquid waste which causes the liquid waste to solidify. These methods are likewise not completely unsatisfactory in that there is no account taken for the leaching of waste material into the surrounding terrain. Examples of such methods are disclosed in U.S. Pat. Nos. 3,196,619 dated July 27, 1965 and 3,274,784 issued Sept. 24, 1966. Moreover, such methods provide no way to retrieve the material if a problem arises.
Clearly, there is a need for a packaging and storing system and module which eliminates the void space but which allows the waste containers to be easily retrieved should a problem arise or a new technology develop. Ideally, such .a module should include a crack-proof barrier capable of chemically and physically arresting the flow of liquid waste, to prevent the migration of radioactive nuclides into the surrounding ground. Finally, it would be desirable if the installation of the void-eliminating barrier did not cause any unwanted floating of the waste containers within the module during the packing operation.